The fire-resistance ratings of construction elements in hours listed in table 3-4 shall be used as a basis for classifying buildings and spaces by construction. Fire-resistance ratings shall be based on the test procedures of reference standard RS3-1 and shall apply to all occupancy groups except as specifically noted. For hazardous occupancies involving an exceptionally high degree of fire risk or an exceptionally high concentration of combustible or flammable contents, the commissioner may increase the requirements of table 3-4.
Table 3-4: Construction Classifications
Notes:
a The area of openings permitted in exterior walls at any story shall be obtained by multiplying the percentage shown in the table by the exterior separation distance in feet, and then multiplying that product by the square-foot area of the facade of that story. Requirements for protected exterior openings shall not apply to churches or to buildings classified in occupancy groups J-2 and J-3. See section 27-331 of article four of subchapter five of this chapter for additional requirements for exterior walls and exterior wall openings.
b Upon special application, the commissioner may permit exterior wall openings to be constructed in excess of the permitted area established by table 3-4 if such openings at the time of their construction are located at least sixty feet in a direct line from any neighboring building except as otherwise permitted by footnote f. Such additional openings may not, however, be credited toward meeting any of the mandatory natural light or ventilation requirements of subchapter twelve of chapter one of this title. If any neighboring building is later altered or constructed to come within the above distance limitation, the affected exterior openings shall immediately be closed with construction meeting the fire-resistance rating requirements for exterior wall construction of the building in which they are located.
c Applies to occupancy groups A, B-1, B-2, and D-1.
d Applies to all occupancy groups other than those described in footnote c.
e See subdivision (i) of section 27-375 of article five of subchapter six of this chapter for additional impact resistance requirements applicable to certain stair enclosures and for certain exceptions to stair enclosure requirements.
f When two or more buildings are constructed on the same lot, and the combined floor area of the buildings does not exceed the limits established by tables 4-1 and 4-2 for any one of the buildings, no fire-resistance rating shall be required for nonbearing portions of the exterior walls of those buildings facing each other, and there shall be no limitation on the permitted amount of exterior openings.
g Fire retardant treated wood complying with the requirements of section 27-328 of article three of subchapter five of this chapter may be used.
h Tabulated ratings apply to buildings over one story in height. In one story buildings roof construction may be of material having 0 hour fire-resistance rating.
i Materials which are not noncombustible, as defined in subchapter two of chapter one of this title, may be used in nonbearing construction elements if they fall into one of the following categories:
1. Materials having a structural base of noncombustible material as defined in subchapter two, and having a surface not over one-eighth inch thick which when tested in accordance with the provisions of reference standard RS 3-2 has a flame spread rating not higher than fifty.
2. Materials which when tested in accordance with the provisions of reference standard RS 3-2 have a surface flame spread rating not higher than twenty-five without evidence of continued progressive combustion, and which are of such composition that surfaces which would be exposed by cutting through the material in any way would not have a flame spread rating higher than twenty-five without evidence of continued progressive combustion.
j Applies to the construction of the street floor and all construction below the level of the street floor in buildings or spaces classified in occupancy group J-2 except where the space below the street floor does not exceed five feet in height.
k Columns supporting the roof of a one-story building shall have the same fire-resistance rating as required for a column supporting one floor in a building of the same construction class.
l Members supporting loads of not more than two floors or one floor and a roof need not have a fire-resistance rating greater than the floor construction fire-resistance requirement in buildings classified in occupancy groups G, H, and J-2, not including unsprinklered spaces of other occupancies, and in fully sprinklered buildings in occupancy groups E and J-1.
m See subdivision (c) of section 27-987 of article one of subchapter eighteen of this chapter for additional impact resistance requirements applicable to certain elevator enclosures.